The goal of the proposed research is to define the developmental program for the pancreatic acinus. A mature, functional acinus is composed of acinar cells, which surround a specialized form of intercalated duct (the centroacinar cells), and the proximal connecting duct (the intercalated duct). We propose that these three cell-types arise as a single developmental unit from a common progenitor cell-type, the terminal tubule cell of the embryonic pancreas. This model is based on the use of new markers that reveal a developmental intermediate reminiscent of the mature acinus, with gene expression boundaries that suggest discrete developmental compartments with specific functions. To examine this model we will define the roles of two key transcriptional regulators, Ptf1a and Nr5a2, through biochemical and genetic analyses. Ptf1a is expressed in two temporal waves during pancreatic organogenesis: at the onset of pancreatic budding and then at super-induced levels during the secondary transition in multipotent precursor cells and nascent acinar cells, where it appears to control differentiation. We will determine the developmental signals and transcription factors that reactivate the expression of the Ptf1a gene for the beginning of acinar development. We have recently shown that Nr5a2 is required during pancreatic development specifically for the formation of acini and is a direct target of PTF1a. Aim 1 will determine the regulatory mechanisms whereby the nuclear receptor NR5A2 controls the early stage of acinar development. Aim 2 will define the regulatory properties of the transcriptional enhancer that reactivates Ptf1a expression in newly forming acinar cells by identifying DNA-binding transcription factors that mediate the activity of the enhancer and determine which of these factors are required for the regulation of Ptf1a expression during embryogenesis and for normal acinar development. Aim 3 will determine the manner in which Wnt and Notch developmental signal are integrated into transcriptional activation of the Ptf1a gene during embryonic development.